Strongly-coupled PbS QD solids by doctor blading for IR photodetection

Abstract

Solution-processed QD solids are emerging as a novel concept for high-performance optoelectronic devices. In this work, doctor blading is proposed for the fabrication of strongly-coupled QD solids from a PbS nanoink for photodetection at telecom wavelengths. The key step of this procedure is the solid-state ligand exchange, which reduces the interparticle distance and increases the carrier mobility in the resulting strongly-coupled QD solid. This is accomplished by replacing the original long oleylamine molecules by shorter molecules like 3-mercaptopropionic acid, as confirmed by FTIR, TGA and XPS. Further, a detailed investigation with XPS confirms the air-stability of the QD solids and the extreme reduction of the principal oxidation product, PbSO₃, from ligand exchange times of 60 s. Finally, the QD solid is tested as an active layer for the fabrication of a Schottky NIR photodetector. The device shows a maximum responsivity of 0.26 A W⁻¹ that corresponds to an internal quantum efficiency higher than 30% at 1500 nm and detectivity around 10¹¹ jones.